The present invention relates to a distance detecting device for detecting a distance of objects with the help of wave signals which are emitted by an object detecting device and reflected from the objects.
While any distance detecting device can be used, the present invention as well as the problems on which it is based are illustrated with a distance detecting device arranged on a bumper of a motor vehicle and using ultrasound echos for distance detection.
In general distance detecting devices for contactless distance detection are known. They are used as parking assisting devices for motor vehicles, in particular a multi-channel measuring systems based on ultrasound. Such distance measurements are based on ultrasound measurements in accordance with the pulse-echo process and as a result have two sending-receiving devices integrated in the bumper of the motor vehicle. The distance measurement is performed by evaluation of the running time of direct echos (for example the transmitting time is simultaneously the receiving time) and the intercepting echos (for example a unit is the transmitting unit and one or several neighboring units are the receiving units).
An acoustic response of ultrasound signals along the bumper (body sound/air sound) is filtered for the evaluation of the signal, to exclude an exchange with actually available echo signals. In other words in the corresponding receiving characteristics, dead time windows are introduced in correspondence with the disturbance signals in which for a predetermined echo mode (for example a predetermined transmitter/receiver combination) no evaluation can take place.
A significant dirtying of the bumpers, for example by snow, ice, dirt, etc. and thereby of the vibration-sensitive membrane of the ultrasound transmitter or receiver increases blinding of the whole system, without however disadvantageously influencing the corresponding sensor individual characteristics.
Since the known systems are unreliable, there is a danger that the driver, in view of an increasing or already reached blinding of the whole system, will react too late or will not react at all.
Accordingly, it is an object of the present invention to provide a distance detecting device, which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a distance detecting device which has transmitter/receiver means for transmitting and receiving wave signals with at least a first and a second transmitting/receiving unit which are spatially spaced from one another, with the first unit performing at least one transmitting functions and a second unit performing at least one receiving function; said both units being formed so that the second unit can receive wave signals emitted by the first unit as response signals, and either the first unit or the second unit can receive the wave signals emitted by the first unit as reflection signals; and an interference determining device for determining at least one characteristic parameter of the response signal received in the second unit and for determining an interference based on the determined characteristic parameter.
The distance detecting device in accordance with the present invention has an advantage as compared with known solutions, since it makes possible recognition of a strong dirtying of the membrane of the transmitting/receiving device at an early time and warning the driver properly about the blinding before a system failure.
The present invention operates so that the disturbance which is an undesired interference signal is provided for detection of the dirtying. In particular, the reduction of intensity of the disturbance with increased blinding, for example accumulation of snow, ice, dirt is utilized.
By a variation of characteristic parameter of for example acoustic signals, an interference can be determined. This usually undesirable additional affect (such signals must be filtered out in a normal operation to exclude an alternation of actual available echo signals) can be used here in order to increase the reliability of the system.
In accordance with a preferable embodiment of the present invention, the interference determination device is formed so that it determines the intensity or frequency of the disturbance signals received in the second unit. If it exceeds a predetermined threshold, then it is possible under certain considerations of the other units to derive an interference criterium participating in the total system. Then a simple interference criterium can be determined.
In accordance with another preferable embodiment of the present invention, for warning the user before a certain interference, a warning device is provided. The user can be informed for example by a visual or acoustic indicator that its system no longer operates reliably.
In accordance with a further preferable embodiment of present invention, the transmitting/receiving device has a third transmitting and/or receiving unit which is spaced from the first and second units spatially, with at least a transmitting function. The three units are defined so that the second unit can determine the wave signals emitted by the first and third units simultaneously as disturbance signals. In the simplest case the first and the third units have identical spacial distances from the second unit.
In accordance with a further preferable embodiment of the invention, the first and second units have different spacial distances from the second unit and a coordination device is provided which is formed so that it coordinates the transmitting functions of the first and third units in time, and the disturbance signals occur simultaneously in the second unit. Thereby an amplification of the disturbance signals and as a result an improved signals/noise ratio is provided.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.